Highly purified FSH, LH, HCG and their subunits are used in the localization of the gonadotropin receptor or receptors in normal and neoplastic ovaries. The hormones are labeled with radioactive iodine or tritium before injection into normal and superovulated rats via tail vein. The ratio of blood level of the hormone to various organs, such as liver, kidney, ovary, muscle, etc is determined to identify the organ or organs which concentrate the hormone. The precise localization of the hormone in the tissue is then established by radioautography, immunohistochemical techniques and electron microscopy. Further confirmation of the receptor site is obtained by in vitro examination of the binding of the labeled hormone by the subcellular fractions (crude nucleii, plasma membrane, mitochondria, microsomes, etc.) of the normal and neoplastic ovary and adrenal obtained from experimental animals and human subjects, when feasible. The specificity of the hormone-receptor interaction is established by the displacement of the bound hormone with unlabeled hormone in vitro, and its inhibition by the use of specific antibodies. We propose to solubilize the receptor containing component and attempt to isolate the receptor protein by the conventional methods of protein purification for physicochemical characterization and to study the receptor site mechanism in steroidogenesis. The steroid and gonadotropin measurements are performed by radioimmunoassay techniques. These studies should contribute in the understanding and control of abnormal growth and secretion of ovaries and adrenals with cancer.